Synthesis of catenanes and molecular knots by copper(I)-directed formationof the precursors followed by ruthenium(II)-catalysed ring-closing metathesis

Catenanes and knots are fascinating molecular systems, but for several deca des these compounds have been regarded as exotic species due to synthetic d ifficulties. We have proposed template strategies based on transition metal s (mostly copper(I)), and this approach has allowed us to make a wide famil y of interlocking rings and knots in the course of the last 15 years. A ver y recent and practically important improve:ment now permits relatively easy preparation of some of these systems with, in some cases, almost quantitat ive yields. The key step is the ring-closing metathesis (RCM) of olefins, u sing the extremely efficient and mild catalysts developed by Grubbs et al. in the last few years, and consisting of ruthenium carbenes. (C) 1999 Elsev ier Science S.A. All rights reserved.